The non-profit Français du Sang-Ile de France thanked Parisians for donating blood and said "10,000 donations" will be needed every day, in a statement. The group said blood drives would be canceled Sunday. The reason for the cancellation was unclear.

USA TODAY's Kim Hjelmgaard spoke with a group of students that were waiting in line outside of a hospital in Paris on Saturday.

"I felt like this is the only thing I could do at the moment to help someone out," Sarah, a student from Philadelphia told Hjelmgaard.

Many waited for five or more hours to donate blood following the attacks, she said.

The Islamic State claimed responsibility Saturday for the series of attacks described by French President Francois Hollande as "an act of war." Hollande vowed to "merciless" response to the militants and declared three days of national mourning.